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Pictures would help. I have never kept tiger barbs before, so I don't know how they normally swim. It could be that something is stressing the majority so they swim with fins clamped, or it could be that the minority has some kind of physical defect that makes them unable to retract their fins. Its not all that far fetched. I've had this occur with another cyprinid, the White Cloud Mountain minnow. Certain fish had their dorsal and anal fins permanently extended, possibly due to bad genetics or something environmental where they were raised. Or it could also be that the ones that keep flaring are the dominant ones.

That was one of my hypotheses, however, even the dominant fish will not flare all the time. They might spend a more than average amount of time with their fins extended, but not all the time, and fin position will vary, sometimes retracted, fully extended, or at half mast. If you are talking about a stiff, rigid fin position that never seems to change, that might be a physical defect.

I've never kept barbs, but I've seen them do that in people's tanks, and it looks pretty much identical to how my pencils act a lot of the time. I'd say probably a dominance thing, basically just them saying that they're alpha fishies.